The invention relates to an apparatus for the plasma-assisted, high rate electron beam vaporization, preferably for the vapor deposition of coatings of compounds on strip-like and plate-like substrates. Typical fields of application are the vaporizing of plastic films with barrier layers for the packaging industry, with scratch-proof coatings for sun-shielding films or foils or with selectively reflecting coatings for heat-absorbing films or foils. Other uses occur in the coating of metallic strips for decorative purposes and for corrosion protection, as well as in the coating of plastic or glass plates for obtaining scratch-proof or selectively reflecting surfaces. However, better coating characteristics also result from the additional plasma action when vapor depositing metallic coatings on different substrates. In particular it is possible to obtain a higher packing density of the coating and therefore improve mechanical, optical and electrical characteristics.
It is known that as a result of plasma action in vacuum coating improved coating characteristics can be obtained. For example, during sputtering, which naturally takes place under plasma action, in general better coating characteristics can be obtained than when vaporizing. However, the coating rates during sputtering are relatively low and are inadequate for many uses. It is possible to achieve higher rates by using the vaporizing procedure.
It is also known to obtain similar coating characteristics to those obtained with sputtering in the case of plasma-assisted vaporizing. Simultaneously with the vapor-deposited material a plasma or the ions extracted from a plasma are made to act on the substrate. The plasma is produced either by ionizing the vapor zone by means of a separately produced low energy electron beam or by igniting an independent discharge between the vaporizer and the substrate (Schiller, S., Heisig, U., Panzer, S., Elekronenstrahltechnologie, VEB Verlag Technik, Berlin, 1976, p.187ff and p.136ff).
The highest coating rates and therefore the lowest coating costs can be achieved by high rate electron beam vaporization. During the vapor deposition of metals coating rates up to 50 .mu.m/s are obtained, but also when vapor depositing compounds coating rates of a few .mu.m/s can be obtained. In order to obtain at such high rates positive effects with regards to the coating characteristics by means of an additional plasma action, correspondingly high plasma densities are required on the substrate. High plasma densities can e.g. be produced with per se known arc discharges. However, it has not hitherto been possible to simultaneously bring into effect the high vaporizing rates and the high plasma densities on the substrate. The high plasma densities lead to such a pronounced spreading or scattering of the electron beam required for vaporization, that it is not possible to achieve the power densities required for high rate vaporization.
It is also known to allow to burn in the vaporizer crucible a plasma arc discharge in addition to the electron beam (Moil, E., Buhl, R., Pulker, H.K., Bergmann, E., Activated Reactive Ion Plating Surface and Coatings Technology 39/40(1989), pp.475-486). However, this additional vaporizer heating does not lead to the coating rates obtained with purely high rate electron beam vaporization. In addition, this procedure is only suitable for vaporizing conductive metals and not for vaporizing insulating compounds. Moreover, the plasma action preferably takes place in the vicinity of the vaporizer crucible and not in the vicinity of the substrate.